The present invention relates generally to wireless communication systems and, in particular, to assigning use of a radio requency communication resource.
Economics play an important role in the design of radio communication systems. Bandwidth is limited and equipment is expensive, and therefore many schemes have been developed for multiplexing multiple users over the same physical channel. One such scheme is time division multiple access (TDMA). In a TDMA system, the radio frequency (RF) signal carrying the information is segmented into intervals called time frames. Each frame is further partitioned into assignable user blocks of time called time slots. During each time slot, the assigned user of that slot is entitled to use the full spectrum of the RF signal. In multi-carrier communication systems, time slots exist in the same point in time on adjacent frequency channels. If two different users of communication units are being served by the same base site and are occupying simultaneously transmitted time slots in adjacent frequency channels, then power from the signal of one of the two different users can potentially couple into the adjacent channel and create undesired interference (i.e., adjacent channel coupled power interference, or ACCP) for the other user.
One solution to the problem of ACCP is to design communication systems with further reduced levels of adjacent channel coupled power. However, ACCP performance is difficult to improve and improvements will generally involve a significant investment in design time and cost and an increase in the component content and cost of the final product. Another solution, proposed in U.S. Pat. No. 4,794,635, issued to Hess, is to measure the communication quality factor, i.e., the signal-to-noise plus interference ratio, for signals already occupying each one of multiple communication channels in adjacent sectors and to select a channel that has the greatest margin between the desired communication quality factor for the channel and the minimum communication quality factor among the signals already occupying the channel. However, Hess does not address the ACCP problem where the assigned signal and the occupying signals are of significantly different signal strengths. If a strong signal and a weak signal with similar communication quality factors couple the same percentage of signal power into the other signal""s bandwidth, the strong signal will create a more significant ACCP problem for the weak signal than will the weak signal for the strong signal. Alternatively, a solution used by large system providers with an abundance of channels to select from is to avoid the use of adjacent frequency channels in the same base site. However, the latter solution results in a less than optimal use of system capacity and is not practical for systems that use a small number of frequency channels.
Therefore, a need exists for a method and apparatus for assigning use of a radio frequency communication resource in a manner such that ACCP is minimized while all communication channels are utilized.